In an aging nuclear power plant, for example, surface inspection and volumetric inspection are required in order to evaluate soundness of its in-core structures. An eddy-current testing (ECT) is known as one method of surface inspection. The ECT has an advantage that inspection can be completed in a short period, because inspection under water can be performed without draining reactor water.
However, there is a case where it may be difficult for ECT to provide good result with high inspection accuracy in dependence upon a variety of an inspection object (which includes an object to be inspected or an inspected object), in such a case that the inspection object by ECT is, for example, an in-core structure such as a bottom portion of a reactor pressure vessel (RPV). In this case, since it is difficult to move an probe (which will be hereinafter referred to as “inspection probe”) for ECT exactly along the surface of the in-core structure as the inspection object, the inspection probe being configured to detect an eddy-current, a distance between the inspection probe and the inspection surface, i.e., lift-off (lift-off distance) is likely to increase or change.
Such increase or change in lift-off leads to reduction in eddy-current detection sensitivity, i.e., flaw (defect) detection sensitivity and occurrence of a false signal which indicates that a flaw is present even though the flaw is not present in (or on) the inspection object. Thus, in general, it is considered to be difficult to perform an inspection of which an inspection object has narrow and complicated parts in shape, such as a bottom portion in RPV, the inspection performed by using ECT.
Accordingly, there is a proposed technique in which actual inspection is performed after storing a contact condition between an inspection probe and an inspection surface in a memory. The stored contact condition is given by performing a teaching process which includes a step of positioning an inspection probe at each point (which will be hereinafter referred to as “flaw detection point”) predetermined in order to detect flaws in/on the inspection object, and a step of setting the contact condition between the inspection probe and an inspection surface at each flaw detection point.